Room Temperature Mechanical Properties And In-Situ Tensile Observation Of ?TiB+TiC+La₂O₃?/IMI834 And ?TiB+La₂O₃?/TC₄ Titanium Matrix Composites

Titanium matrix composites?TMCs?with discontinuous reinforcement possess many advantages,such as good mechanical properties,superior resistant to corrosion and easy-fabrication.However,the low ductility limits the wide application of the material.In present work,several experiments,including microstructure observation,tensile test at room temperature and in-situ tensile test are conducted on?TiB+La₂O₃?/TC4 and?TiB+TiB+La₂O₃?/IMI834 titanium matrix composites.The impact of reinforcements content on the microstructure,tensile properties at room temperature and fracture behavior are analyzed.The microstructure evolution at the crack tip and the propagation of crack are studied,so that the effect of reinforcement content on the fracture behavior of material can be revealed.With hot working and aging,the microstructure of the matrix in?TiB+La₂O₃?/TC4 and?TiB+TiB+La₂O₃?/IMI834 TMCs is basket wave structure.Reinforcements of TiB is in the shape of short fibers,TiC is granular and La₂O₃ is either nano-scale particles or aggregated.In?TiB+La₂O₃?/TC4,reinforcements disperse homogenously through the matrix and roughly align along the forging direction.However,in?TiB+TiB+La₂O₃?/IMI834,lots of TiB short fibers are broken at forging and stacking faults can be observed.When the reinforcement volume fraction increases,the microstructure of the matrix can be refined.With the increasing of reinforcement content,the tensile strength of?TiB+La₂O₃?/TC4 increases while the elongation decreases.?TiB+La₂O₃?/TC4 with 1.2 vol.%of reinforcements possesses the highest elongation rate?11.1%?.And with 4.8 vol.%of reinforcements,it has the highest tensile strength?1080MPa?.The increasing in strength is mainly due to the enhancement of grain refinement effect and load-bearing effect.However,the tensile strength and elongation of?TiB+TiB+La₂O₃?/IMI834both decreases greatly due to the defects introduced at hot forging process.Quasi-cleavage fracture is the dominating fracture mechanism for?TiB+TiB+La₂O₃?/IMI834.Tear ridge and river pattern can be observed at the fracture of three kinds of materials,and small dimples only exist in material with 0.5 vol.%of reinforcements.The existing defects in TiB and TiC reinforcements develop into micro-cracks and expanding rapidly,leading to the failure of samples.The failure of?TiB+La₂O₃?/TC4 is a combination of ductile fracture and brittle fracture.And it's mainly caused by the propagation and gathering of microcracks and slip bands after the fracture of reinforcements.As higher volume fraction of reinforcements introduces more cracks into the matrix,it facilitates the coarsening and connection of adjacent cracks and slip bands.Therefore,the ductility of composites decreases.